In theory, that could happen, but the chances are very small. The most important thing to know is that your investments would still be safe. They are kept separate from UpToMore B.V. and are held by an independent foundation.
This foundation exists solely to hold your investments and cannot use them for anything else. Every day, an independent party (the “depositary”) checks whether the money you deposit with UpToMore is securely stored in the name of the foundation. If there is any doubt, the depositary reports this to the AFM (Dutch Authority for the Financial Markets), the financial regulator in the Netherlands.
Only in the unlikely event of fraud could it happen that money is not registered in the name of the foundation. For this rare scenario, there is an additional safety net: the Investor Compensation Scheme, which covers up to €20,000 per person.